Most of the cancer chemotherapy agents currently in clinical use are cytotoxins. That is, they kill cancer cells by interfering with cell division, e.g., by damaging the DNA of dividing cells, or by inhibiting the production of the deoxynucleotides that are necessary to replicate DNA during cell division. The usefulness of most cancer chemotherapeutic agents is limited by their systemic toxicity and, in many cases, the development of resistant tumor cells.
An example of such a chemotherapeutic agent is doxorubicin. Although doxorubicin is an effective and widely used cancer chemotherapeutic agent, its clinical utility is significantly limited by a dose-dependent cardiotoxicity and the frequent emergence of resistant tumor cells. One approach to circumventing these limitations has been to increase antitumor cytotoxicity by coupling the drug to various carriers such as monoclonal antitumor antibodies (Diener E, Diner U E, Sinha A, Xie S, Verdigis R (1986) Science 231: 148), albumin (Hatano T, Ohkawa K, Matsuda M (1993) Tumor Biol. 14: 288; Gabor F, Wollmann K, Theyer G, Haberl I, Hamilton G (1994); Anticancer Res. 14: 1943), and transferrin (Berczi A, Barabas K, Sizensky J A, Faulk W P (1993) Arch. Biochem. Biophys. 300: 356; Fritzer M, Barabas K, Szuts V, Berczi A, Szekeres T, Faulk W P, Goldenberg H (1992) Int. J. Cancer 52: 619; Faulk W P, Taylor C G, Yeh C G, McIntyre J A (1990) Mol. Biother. 2: 57; Thorstensen K, Romslo I (1993) Scand. J. Clin. Lab. Invest. 53 (Suppl 215): 113). These strategies have aimed to decrease the clinically effective dosage of the drug and, thereby, to lessen undesirable side effects such as cardiac toxicity. Crosslinking doxorubicin to transferrin has been found to yield preparations with enhanced cytotoxicity (Lai B-T, Gao J-P and Lanks K W (1997) Cancer Chemother. Pharmacol.).
The present invention provides for the synthesis of glutaraldehyde modified doxorubicin and other glutaraldehyde-modified chemotherapeutic agents. The glutaraldehyde modified compounds of the invention have a predicted structure, based on the method used to synthesize them and the known reactivity of the reagents used in the method, of R--NH--CO--(CH.sub.2).sub.3 --CO--NH(CH.sub.2).sub.2 OH, where R--NH-- is the portion of the derivative compound comprising the parent compound.
Various modifications of doxorubicin with glutaraldehyde have been reported in the prior art. A doxorubicin derivative where the terminal aldehyde group was not blocked with ethanolamine was prepared by Page et al., U.S. Pat. No. 5,208,323, but the antitumor efficacy of this compound was not evaluated. Glutaraldehyde-crosslinked polymers of daunorubicin have been prepared by Relyveld, U.S. Pat. No. 4,625,019, and appear to have antitumor activity upon spontaneous hydrolysis. However, the compounds produced by Relyveld are not synthesized by the method used to produce the derivatives of the present invention. Tong et al., in U.S. Pat. No. 4,202,967, produced a N,N-pentamethylene derivative of doxorubicin by reaction of glutaraldehyde with doxorubicin. This reaction is done without subsequent addition of ethanolamine, and results in a cyclic pentamethylene adduct. Further, the compounds disclosed by Tong, et al. exhibited antitumor activities that were decreased about four-fold, on a weight basis, relative to the parent doxorubicin or daunorubicin compound. Thus, there remains a need in the art for glutaraldehyde-modified chemotherapeutic agents, and particularly glutaraldehyde-modified anthracyclines such as doxorubicin, that display antitumor efficacy at lower doses than the parent compounds. There is also a need in the art for chemotherapeutic agents that are effective against tumor cells that have attained resistance against conventional, or unmodified, chemotherapeutic agents.